Comments stopped not working

Several of my blog readers emailed to let me know the comment function isn’t working anymore. Unfortunately, I can’t pinpoint the error b/c comments work fine for me in both Firefox and IE. (And the spam gets through, too.)

I’ve requested more specifics from the readers who emailed (what kind of error they get and browser they’re using). Lacking that info, what might be wrong? Again, everything works when I leave a comment. I haven’t changed themes lately.

People are attempting to comment and, when the attempt fails, emailing me (via my contact page) that the blog would not process the comment. No trace of a “failed” comment appears in my Dashboard. The only way I know it’s not working is from the (regular) emails I receive from readers telling me their comment wouldn’t post.